Ship stern fitted with twin-screw propulsion

ABSTRACT

The hull of a ship with twin propellers, varying in crosssection from approximate V-shape at the aft end via trapezoidal intermediate profiles to a U-shape at the midsection, forms a pair of bulb-shaped excrescences which surround the propeller shafts and are faired into the hull surface rearwardly of a bulkhead separating the engine room from an adjoining cargo compartment. The two bulbs define between them a shallow tunnel of progressively decreasing height, extending over not more than 15% of the length of the ship.

United States Patent Klasic [451 Aug. 1, 1972 [54] SHIP STERN FITTED WITH TWIN SCREW PROPULSION [72] lnventor: Mladen Klsic, Pula, Yugoslavia [73] Assignee: Ulianik brodogradilkte l tvornica Dizel motorafula u sastavu zdruzenog poduzeca Jadranbrod, Pula, Yugoslavia [22] Filed: April 20, 1970 [21] Appl. No.: 30,085

[30] Foreign Application Priority Data April 21, 1969 Yugoslavia ..P 972/69 521 US. Cl ..114/57 [51] Int. Cl. ..B63b l/08 [58] Field of Search ..114/57, 56

[56] References Cited UNITED STATES PATENTS 3,565,029 2/1971 Smit ..114/57 1,034,626 8/1912 Von Koppen ..114/57 1,779,041 10/1930 Hogner ..114/57 2,729,182 1/1956 Tommasi ..114/57 l/1970 Messerschmidt ..114/56 Primary Examiner-Andrew H. Farrell Attorney-Karl F. Ross [57] ABSTRACT The hull of a ship with twin propellers, varying in cross-section from approximate V-shape at the aft end via trapezoidal intermediate profiles to a U-shape at the midsection, forms a pair of bulb-shaped excrescences which surround the propeller shafts and are faired into the hull surface rearwardly of a bulkhead separating the engine room from an adjoining cargo compartment. The two bulbs define between them a shallow tunnel of progressively decreasing height, extending over not more than 15% of the length of the ship.

4 Claims, 4 Drawing Figures mm; 1 m2 FIG. 3

M/aden Klasi l N VEN TOR.

SHIP STERN FITTED WITH TWIN-SCREW PROPULSION l. FIELD OF THE INVENTION My present invention relates to a ship stern fitted with twin-screw propulsion, advantageously for ships of over 200,000 tons deadweight.

2. BACKGROUND OF THE INVENTION There are known single-screw and twin-screw propulsion ships. Comparative analyses of both kinds of propulsion in relation to large ships of conventional shape allow the following conclusions. For big ships of about 100,000 tons dead weight, twin-screw propulsion is less effective than single-screw propulsion, whereas for ships of over 200,000 tons dead weight it can be expected that both kinds of propulsion are equivalent provided that the number of propeller revolutions of a twin-screw ship equals the number of revolutions of a single-screw ship. Up-to-date ships of this size are provided with propulsion engines having a power of 30,000 to 35,000 HP and 80 to 90 revolutions per minute. With the above condition fulfilled, it can be assumed that twin-screw propulsion of a ship with over 300,000 tons deadweight is preferable to single-screw propulsion.

The main deficiency of all known constructions of twin-screw or multiple-screw ships lies in the fact that ships of this kind could not perform at the same speed as single-screw ships with propulsion engines of the same power, notwithstanding the fact that the initial investment for the twin-screw propulsion is much higher. The second drawback of conventional twin-screw constructions resides in the need for a longer engine room than normally required when using a single-screw propulsion engine of the same power. This means an essential loss of available cargo space, less efficient trimming and higher requirements on the strength of the ship hull. These drawbacks are particularly noticeable with catamaran-type vessels, i.e., with ships having a distinct dual body and a deep intermediate tunnel.

3. OBJECTS OF THE INVENTION The object of the invention is to avoid the imperfections of known constructions and to provide, in a ship powered by twin-screw propulsion, greater safety of operation, better maneuverability, improved course stability and reduction of insurance costs.

4. SUMMARY OF THE INVENTION More particularly, given a ship using twin-screw propulsion and having an engine room of a length equal to or shorter than that of a comparable single-screw propulsion vessel, my invention aims at providing a hydrodynamically suitable shape of the ships hull, chiefly at the stern, allowing the attainment of a speed at least equal to that of the single-screw ship.

According to the invention this task is solved by designing the bottom of the ship, in a region extending over not more than percent of the total length from the stern toward the middle of the ship, as a shallow tunnel ending in the vicinity of the front bulkhead of the engine room. The tunnel walls merge symmetrically on both sides into drop-shaped bulbs enshrouding the propeller shafts, these excrescences extending forwardly from the propellers and terminating in a section of bilge radius at the end of the tunnel directed toward midships. Each bulb envelops an imaginary knuckle line defined as the locus of the points of intersection of lines tangent to the side and bottom surfaces of successive cross-sections of the ships hull which vary progressively from a distinct U-shape in the middle of the ship to a trapezoidal shape with upwardly divergent sides and, at the end of the stern, approach a V-shape.

5. DESCRIPTION OF THE DRAWING An embodiment of the invention will now be described in greater detail with reference to the accompanying drawing wherein:

FIG. 1 shows a longitudinal section of the stern of a ship taken in its longitudinal plane of symmetry, i.e., on the line I I of FIG. 2;

FIG. 2 is an end view, in the direction of the arrow II of FIG. 1, of half the stern of the ship;

FIG. 3 is a bottom view of half the stern of the ship in the direction of the arrow III of FIG. 1; and

FIG. 4 is a cross-section through a part of the engine room of the ship, taken on the line IV IV of FIG. 1.

6. SPECIFIC DESCRIPTION In the drawing the reference number 1 designates the stern part of a ship which is separated by a forward bulkhead 3 of its engine room from the cargo room 2. The lower part of the ships hull forms drop-shaped bulbs excrescences 4 which progressively decrease in cross-section toward a final section supporting a propeller 5 with a hub 6 centered on a horizontal axis m. The ships rudder 7 is mounted on a support 9. The reference number 8 marks the main engine placed in the cavity of the bulb 4. The two bulbs define between them a tunnel whose front part 10a (see FIG. 2) is deeper than its rear part (see FIG. 4) 10b. The deck of the ship is marked by p.

The profile of the ships hull changes progressively from an approximate V-shape at the aft end, represented by a flat surface Z conventionally referred to as a transom, to a U-shape at the midsection, as best seen in FIG. 4 which shows the outlines of successive cross-sections in transverse planes P P P P (cf. FIGS. 1 and 2). Line g is a knuckle line or chine, at the junction of the lateral and bottom surfaces of the hull, whose imaginary extension g in the region of bulb 4 is enshrouded by that bulb until its emergence therefrom at a point beyond plane P (ahead of bulkhead 3) where the bulb is faired into the hull. The outer and inner boundaries of the bulb, i.e., the lines along which its circumference merges with the general outline of the hull, have been designated k, and k These boundaries, which may be either sharp or rounded, extend along the bottom and side surfaces, respectively, of the aft portion of the hull and converge at a point K, lying on the knuckle line g, from which a terminal ridge b extends across the rear end of each bulb to a tip T at the propeller axis m. Lines k, and k disappear in the region of intermediate transverse plane P i.e., an area where the hull has its substantially trapezoidal transitional profile as seen in FIG. 2, at which point the bulbs 4 are faired into the hull surface.

The roof of the tunnel 10a, 10b between the two bulb-shaped excrescences 4 slopes downwardly,

toward the front, at a small angle of not more than to merging into the ships bottom at a location spaced from the aft section Z by not more than 10 to 15 percent of the overall length of the ship. The propellers or screws 5 are counterrotated in such a sense that their motion is directed toward the tunnel. The design of the bulbs and of the intervening tunnel results in a strong rotation of the wake stream toward the propellers, thereby increasing the propulsion efficiency of the ship s drive.

It is understood that the invention is not limited to ships equipped with internal-combustion piston engines, but also applies to ships equipped with turbine driving units.

1 claim:

1. A stern structure for a twin-screw ship, comprising a hull with an aft portion varying in cross-section from approximately V-shape at its aft end to U-shape amidships with intermediate transitional profiles of upwardly diverging trapezoidal shape, said aft portion forming a pair of bulb-shaped excrescences disposed symmetrically on opposite sides of a longitudinal plane of symmetry, said excrescences being faired into the hull surface in the region of said transitional profiles and converging from said region to a rear end; a propeller mounted at said rear end on each of said excrescences; and drive means for each said propeller inside the respective excrescence.

2. A structure as defined in claim 1 wherein each of said excrescences comes to a tip at the location of said propeller and forms a ridge extending obliquely upwardly and inwardly toward said plane of symmetry from said tip to a point of intersection of a pair of boundary lines with a knuckle line at the junction of a bottom hull surface and a lateral hull surface, said boundary lines being the respective junctions of the excrescence with said bottom and lateral hull surfaces.

3. A structure as defined in claim 2 wherein said excrescences define between them a shallow tunnel with a forwardly and downwardly sloping roof merging into the hull bottom in the region of said transitional profiles.

4. A structure as defined in claim 3 wherein said drive means are operable to counterrotate the propellers in the direction of said tunnel. 

1. A stern structure for a twin-screw ship, comprising a hull with an aft portion varying in cross-section from approximately V-shape at its aft end to U-shape amidships with intermediate transitional profiles of upwardly diverging trapezoidal shape, said aft portion forming a pair of bulb-shaped excrescences disposed symmetrically on opposite sides of a longitudinal plane of symmetry, said excrescences being faired into the hull surface in the region of said transitional profiles and converging from said region to a rear end; a propeller mounted at said rear end on each of said excrescences; and drive means for each said propeller inside the respective excrescence.
 2. A structure as defined in claim 1 wherein each of said excrescences comes to a tip at the location of said propeller and forms a ridge extending obliquely upwardly and inwardly toward said plane of symmetry from said tip to a point of intersection of a pair of boundary lines with a knuckle line at the junction of a bottom hull surface and a lateral hull surface, said boundary lines being the respective junctions of the excrescence with said bottom and lateral hull surfaces.
 3. A structure as defined in claim 2 wherein said excrescences define between them a shallow tunnel with a forwardly and downwardly sloping roof merging into the hull bottom in the region of said transitional profiles.
 4. A structure as defined in claim 3 wherein said drive means are operable to counterrotate the propellers in the direction of said tunnel. 